Am Fam Physician. 2007;76(5):711
Background: Osteoporosis is arbitrarily defined as a bone mineral density (BMD) that is 2.5 standard deviations (SDs) or more below the mean in younger women, as measured at the femoral neck. Osteopenia is defined as a BMD that is 1 SD or more below the younger women's mean. Using these cutoffs, it is estimated that 17 percent of U.S. women 50 years and older will be diagnosed with osteoporosis and 50 percent of white U.S. women who are postmenopausal will be identified as having osteopenia. Because there is only fair correlation in BMD measurements at different sites, the convention is to use the lowest score from measurements taken at the femoral neck, total hip, or lumbar spine. However, this practice increases the number of women diagnosed with osteopenia without providing additional predictive information about fracture risk, and therefore is no more useful than the femoral neck measurement alone.
Fracture risk increases with age and lower BMD; however, white race, female sex, previous fractures, stroke, and deconditioning or weakness also increase fracture risk. Alcohol consumption of one or two drinks daily may decrease the risk, but consumption of greater amounts increases it. Other modifiable risk factors include smoking and poor visual acuity. Although low weight is associated with fracture risk, it is not a meaningful risk factor when the BMD has been measured because weight is merely a marker for BMD. Women with a history of fractures or radiographically confirmed fractures have a fourfold risk of fracture, and pharmacologic treatment in these women is indicated.
Recommendations: Weight-bearing exercise improves BMD and decreases fall and fracture risk. The optimal types and durations of such exercise are not known. Calcium and vitamin D supplementation are beneficial in older women, but their benefit in younger women is unclear. One recommendation for women in middle age is 800 IU vitamin D and 500 mg calcium daily, to supplement the 700 IU calcium provided in the average diet.
All medications improve BMD and reduce vertebral fracture risk in women who are postmenopausal and have osteoporosis or low BMD, but not all treatments reduce nonvertebral and hip fracture risk. Estrogen is the only treatment that has been shown to reduce nonvertebral fracture risk in women with osteopenia. Alendronate (Fosamax) reduces nonvertebral fracture risk in women with osteoporosis but not in women with higher BMDs (i.e., T-scores greater than −2.5). Decisions about pharmacologic treatment for fracture prevention depend on fracture risk and patient preference.
Other recommendations include starting BMD testing at age 65, or sooner in patients with multiple risk factors. Because the difference in BMD between two tests must be at least 4 to 5 percent to be a reliable indication of change, women with osteopenia and no other risk factors should wait five to 10 years before being retested. Factors influencing the testing interval include the likelihood that the bone loss is rapid (e.g., immediately after menopause) and whether the result would influence management. Testing is warranted in patients of greater age if their life expectancy is long enough for them to benefit from treatment—usually two to three years.
Finally, it is likely that use of bisphosphonates is safe for at least 10 years. A conservative approach is for patients at lower risk to have a five-year break from the drug after five years of use. In the future, T-score definitions are likely to be replaced by fracture risk estimates as a basis for treatment recommendations.